Visiting Medical Students

Thank you for your interest in enrolling as a visiting student in Radiation Oncology at the Perelman School of Medicine at the University of Pennsylvania. Please click on the links below to find out more information about the program and our application process. Note that this application is only for U.S. and Canadian Medical Students.

The Four "R’s" of Radiation Biology

Redistribution: Cells "redistribute" from radioresistant phases (e.g. S phase) of the cell cycle to more radio-sensitive cell cycle phases (e.g. M phase) in between radiation fractions Hyperfractionated radiotherapy (increased number of XRT fractions increases the probability of cells being in M phase during a treatment).

Reoxygenation: Cells may go from a hypoxic (and thus radioresistant) environment to a well-oxygenated state as a course of treatment proceeds Hyperfractionated radiotherapy; hypoxic cell sensitizers; carbogen or hyperbaric oxygen during XRT.

Repopulation: Cells may respond to the death of adjacent cells by "accelerated repopulation" Accelerated radiotherapy kills off cells before they gain the opportunity to repopulate.

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Glossary of Terms Related to Radiation Therapy

Adjuvant: Generally refers to postoperative therapy. However, chemotherapy given after "definitive" radiotherapy would also be considered adjuvant.

Blocks: Thick shields made of a lead-like alloy which can be shaped for each patient to "block" portions of their anatomy that would otherwise fall into the radiation field. In the treatment of head and neck cancer, for example, every attempt is made to block as much CNS tissue as possible.

Brachytherapy: radiotherapy given in the form of radioactive sources placed directly into or around a patient’s tumor. This may be given interstitially (sources imbedded directly into tissue) or intracavitary (sources laid into a cavity such as the nasopharynx.

Cobalt-60 therapy: A form of external beam radiotherapy in which the source of radiation is not x-rays, but gamma rays emitted from a machine containing radioactive Cobalt-60.

Conedown: Shrinking the field size sometime during the course of radiotherapy, to take advantage of the decreasing size of tumor during treatment and to minimize the amount of toxicity of treatment. For example, a patient may begin radiotherapy with a 15 x 15 cm field and then have a conedown midway through treatment to a 10 x 10 cm field.

Conformal Radiotherapy: The use of extremely sophisticated imaging studies and dosimetry to design radiation fields that "conform" precisely to the shape of a patient’s tumor. Conformal radiotherapy usually uses smaller "safety margins" around a patient’s tumor, a larger number of fields, and less prophylactic radiotherapy of clinically uninvolved lymph node areas.

Consolidative: Refers to radiotherapy given after a maximal or complete response to chemotherapy, as is often done in the treatment of lymphomas.

Course: A series or program of radiation treatments or fractions with a specific goal in mind for a patient, e.g. a seven-week course of daily radiotherapy to the lung for attempted cure.

Definitive: Refers to radiotherapy given with the intention of cure without radical surgery. May be given with other non-surgical treatment such as chemotherapy.

Dosimetry: The process of optimizing the radiotherapy fields and dose by calculating the radiation dose to be received by a tumor and/or normal tissues in a radiation field(s). Physicists and "dosimetrists" work with the radiation oncologist in comparing possible radiation treatment plans with the goal of maximizing the radiation dose to the tumor while minimizing dose to normal tissue, often requiring sophisticated computer programs. Dosimetry can be described as the radiotherapy version of pharmacokinetics.

External beam radiotherapy (x-ray therapy): radiotherapy given from a machine (usually a linear accelerator) which produces a high-energy x-ray beam which is then aimed at a patient’s tumor and/or suspected tumor areas.

Field: An area at which a radiotherapy beam is directed, usually described as a rectangular shape, in cm (e.g. 10 x 14 cm). "Blocks" are often used to further customize the shape of a field. A single fraction of radiotherapy may include multiple fields, typically two to four.

Fraction: A single radiation therapy session, usually given over one to three minutes. A fraction may consist of one or multiple "fields," and any dose, as prescribed by the radiation oncologist. Most courses of radiotherapy involve one fraction per day, Monday through Friday, over one to seven weeks, although an infinite number of possible fractionation schedules are possible.

Radiation Therapy Oncology Group (RTOG): A National Cancer Institute-sponsored multicenter clinical trials cooperative group which performs studies related to radiation therapy, including many lung cancer studies.

Radiosensitizers: Drugs or other treatments which increase the cellular response to radiotherapy. Many chemotherapeutic drugs have radiosensitizing properties.

RTOG: See Radiation Therapy Oncology Group.

Safety Margin: A margin of "normal-appearing" tissue which is added onto the visible tumor area for the purposes of radiation planning. Typically 1.5-2 cm in all dimensions is added, to account for microscopic extension of tumor cells and the possibility of slight patient motion during treatment.

Simulation: A detailed planning session for radiation therapy, which "simulates" but does not actually deliver a radiation treatment. Simulation consists of immobilization of the patient in an appropriate position for radiation therapy, marking the patient’s skin, localizing the area to be treated under fluoroscopy, taking radiographs of the area to be treated, and taking measurements of the patient’s contour for dosimetry purposes.